Method and apparatus for recovering hydrocarbons from gaseous mixtures by freezing



June 20, 1950 R. SLOBOD 2,51

METHOD AND APPARATUS FOR RECOVERING HYDROCARBONS FROM GASEOUSMIXTURES BY FREEZING Filed April 15, 1947 T??? 9 :QQQL

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,2. Ca- (Mg Robert L.SLObod I B 12M 5 53M! Attorney Patented June 20, 1950 METHOD AND APPARATUS FOR RECOVER- ING HYDROCARBONS FROM GASEOUS MIXTURES BY FREEZING Robert L. Slobod, Dallas, Tex., assignor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Application April 15, 1947, Serial No. 741,444

9 Claims. (01. s2 175.5)

The present invention relates to improvements in method and apparatus for separating components of a gaseous mixture at low temperature, and relates more particularly to the recovery of normally gaseous hydrocarbons from gaseous mixtures by freezing out the hydrocarbons from non-condensible gases.

The present inventionis particularly adapted to the recovery of normally gaseous hydrocarbons from admixture with air or other gases, especially soil gases obtained in geochemical prospecting for petroleum deposits.

In geochemical prospecting, it has been common practice to sink a shallow bore in the earth's surface and to aspirate from the lower portion of the bore, the soil gases which accumulate therein, precautions being taken to prevent insofar as possible, the entrance of surface air which would contaminate the soil gas and interfere with the interpretation of the results of the analysis thereof. To recover the hydrocarbon content of the soil gas, and particularly ethane, it has been the practice to pass the soil gas through a freeze-out tube chilled by immersion in liquid nitrogen, the temperature attained being approximately 196 C. at atmospheric pressure. By such means it had been thought that all of the hydrocarbon content, including ethane, had been recovered from the soil gas. However, it has now been found that at the temperature of liquefied nitrogen (196 C.), a considerable quan ity of the ethane was not recovered from the soil gas by freezing, but passed through the freeze-out tube with non-condensible gases and was lost. As a result, analysis of the recovered hydrocarbons led to incongruous results due to the absence of a substantial proportion of the ethane which should have been present in the hydrocarbon mixture recovered from the soil gas.

In order to overcome this difficulty, an improved apparatus and method has been devised wherein the substantially complete recovery of hydrocarbons, including'ethane, may be readily achieved. While the present invention is particularly applicable to the freezing out of hydrocarbons from soil gas, it is also adaptable in any case where it is necessary to recover components of a gaseous mixture or to separate condensible components from non-condensible components.

In accordance with the present invention there is provided a method and apparatus wherein a gaseous mixture containing components which it is desired to recover is passed through a freezeout tube in indirect heat exchange with a cold liquid at atmospheric pressure which in turn is cooled by indirect heat exchange with a liquid refrigerant vaporizing under reduced pressure. By this means it is possible to obtain a temperature in the freeze-out tube considerably lower than by simply immersing such tube in the refrigerant maintained at atmospheric pressure. For example, liquefied nitrogen at atmospheric pressure will provide a temperature of about -196 C. (-320 F.) whereas the same refrigerant used in accordance with the present invention will provide temperatures as low as 210 C. (-346" F.). Furthermore, the apparatus employed for accomplishing this result is of simple construction and permits the ready introduction and removal of the freeze-out tube, which feature is of considerable importance to the operator and was not available in the freeze-out systems heretofore used.

The present invention may be further understood with reference to the accompanying drawing which illustrates, partially in cross-section, an apparatus suitable for carrying out the separation of components from a gaseous mixture.

Referring to the drawing, I represents a cham- I ber suitable for containing a liquid or liquefied refrigerant such as liquefied nitrogen. The chamber, as shown, comprises a vacuum bottle or Dewar flask having an inner wall and an outer wall of glass, the annular space between the walls being evacuated to prevent heat transfer. If desired, any well insulated vessel may be employed in lieu of the vacuum bottle, for example, a glass, metal, or ceramic vessel externally insulated by a jacket of relatively non-heat conducting material may be utilized. Disposed within chamber I and spaced from the walls thereof, is a tubular container 2, preferably of glass, such container being open to the atmosphere at the upper end 3. Surrounding the upper portion of container 2 and concentrically spaced therefrom is a collar 4, the upper end of which is sealed to the container adjacentits open end 3. The lower end of collar 4 is open and communicates with the interior of chamber I. A gasket or apertured plug 5 of resilient material such as rubber is positioned between collar 4 and the inner wall of chamber I, such plug being removable and serving to temporarily seal the container 2 in the chamber I. Connected to the upper section of collar 4, above plug 5, is an inclined tube or manifold 6 which communicates via the annular space between the collar 4 and container 2, with chamber I.

At-, tached to the manifold '6 is a pressurefreliei means such as valve I comprising a spheric l, casing containing a ball 8 and a stop 9 for pr venting the ball from seating against outlet I0. Valve 1 functions to rapidly vent refrigerant; vapors in the event of the sudden or explosive liberation thereof in chamber I, and likewise functions to prevent the intake of air when chamber I is being maintained under reduced pressure.

Also attached to manifold 6 is a 2-way valve or stopcock II' having tube I2 for connection to a vacuum pump (not shown) and tube I3 for admitting air to chamber I when it is desired to bring chamber I to atmospheric pressure. Connected at the end of manifold 6 is an inlet I4 provided with a stopper I5 of rubber or other material. Liquefied refrigerant is introduced into chamber I via inlet I4 and manifold 6, as required. Disposed within tubular container 2 is a conventional freeze-out tube comprising a hollow body I5, preferably of glass, provided with a gas inlet tube I1 and an outlet tube I8.

The operation of the apparatus, for example, in recovering condensible hydrocarbons from soil gas, is as follows:

The apparatus is assembled as shown in the drawing, and liquefied nitrogen is introduced into chamber I to the level indicated by line I9 by means of inlet I4 and manifold 6, the inlet I4 then being closed with stopper I5. Liquefied nitrogen is also introduced into the tubular container 2 to the level indicated by line 20 via the open end 3. Explosions resulting from the vaporization of the confined liquefied nitrogen in chamber I are prevented by pressure-relief valve I which vents the refrigerant vapor, the ball 8 being unseated by a surge of vapor, with reseating after pressure is relieved. At this stage a temperature of about -196 C. is available in the liquefied nitrogen in chamber I and tubular container 2. Valve II is then adjusted to connect tube I2 to a vacuum pump (not shown) and a constant vacuum of, for example, 27 inches of mercury, is maintained in chamber I above the level of the liquefied nitrogen contained therein. vaporization of a portion of the liquefied nitrogen in chamber I under the reduced pressure lowers the temperature of the remaining liquefied nitrogen to approximately 2l0 C. The liquefied nitrogen in tubular container 2 is slowly cooled as a result of the low temperature produced in the refrigerant contained in chamber I, and after a period of about to 30 minutes the temperature of the liquefied nitrogen in tubular container 2 is also approximately 2l0 G. Since the wall of the freeze-out tube I6 is in direct contact with the liquefied nitrogen in container 2, such wall is likewise at about -210 C. To recover condensible hydrocarbons from a gaseous mixture, for example, soil gas comprising air and the lower aliphatic normally gaseous hydrocarbons, such gaseous mixture is continuously introduced into the freeze-out tube I6 by means of inlet tube I'I, the pressure in the freeze-out tube preferably being maintained somewhat below atmospheric, for example, 10 pounds per square inch abs., in order to prevent condensation of air. In passing through the freeze-out tube, condensible hydrocarbons deposit on the wall of the freeze-out tube, while air or other gases noncondenslble at the temperature and pressure prevailing in such tube are removed therefrom through outlet tube I8. After the desired volume of soil gas has been passed through the freezeout tube and the hydrocz bon content thereof deposited therein, the tube may be removed from the liquefied nitrogen in container 2 and warmed up to room temperature, at which point the volatilized hydrocarbons can be pumped from the freeze-out tube into an appropriate receiver and thereafter subjected to analysis by conventional methods. At such time as it maybe necessary to replenish the supply of refrigerant in chamber I, valve I I is adjusted so that the vacuum pump is disconnected and air is admitted into chamber I via tube I 3 and manifold 6, thus restoring atmospheric pressure in chamber I. Stopper I5 is removed and additional liquefied nitrogen is introduced through inlet I4 and manifold 6. The stopper is then replaced and the evacuating cycle is repeated. When it is desired to conclude the operation, valve II may be adjusted so that air is admitted through tube I3, thus bringing chamber I to atmospheric pressure and substantially reducing the vaporization of the refrigerant in chamber I.

Exemplary of the results obtainable in accordance with the present invention, a known volume of air containing 2.80 parts of ethane was pumped through the apparatus above described over a period of 5 minutes, using liquefied nitrogen at reduced pressure as the refrigerant, the temperature in the freeze-out trap being 210 C. The amount of ethane recovered was 2.80 parts, indicating no loss through failure to condense out at 210 C. The run was repeated using a known volume of air containing 7.78 parts of ethane. In this case the freeze-out temperature was maintained at 196 C. by means of liquefied nitrogen at atmospheric pressure. The amount of ethane recovered was 5.34 parts, indicating a loss of 2.44 parts through failure to condense out at 196 C.

The'method and apparatus of the present invention may be used in the recovery of no mally gaseous hydrocarbons such as methane, ethane, ethylene, propane, propylene, and the butanes and butylenes, acetylene, butadiene, or mixtures of 2 or more thereof, as well as in the recovery of other organic or inorganic gases including compounds of sulfur, or of oxygen, or of nitrogen, or halogen or halogen compounds, etc. The refrigerants employed in the present invention include liquefied oxygen, nitrogen, hydrogen, argon, helium, krypton, and liquid air, liquefied methane or ethylene, ammonia, sulfur dioxide, etc, the nature of the refrigerant chosen being dependent upon the character of the substance to be recovered and the temperature required. The liquid employed in tubular container 2 may be of the same or different composition than that used as refrigerant in chamber I, provided that the freezing point of such liquid be sufiiciently low that the liquid will not completely solidify at the freeze-out temperature required.

I claim:

1. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant, a container open at one end disposed in said chamber, a. collar spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, and means associated with said collar for permitting a retainer adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communicating with said collar, and means associated with said manifold for permitting a reduction of pressure in said chamber.

3. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant,- a container open at one end disposed in said chamber, a collar spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communicating with said collar, means associated with said manifold for permitting a reduction of pressure in said chamber and for restoring atmospheric pressure in said chamber, and means associated with said manifold for rapidly venting refrigerant vapors from said chamber.

4. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant, a container open at one end disposed in said chamber, a collar spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communicating with said collar, means associated with said manifold for permitting a reduction of pressure in said chamber and for restoring atmospheric pressure in said chamber, means associated with said manifold for rapidly venting refrigerant vapors from said chamber, and means associated with said manifold for introducing refrigerant into said chamber.

5. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant, a container open at one end disposed in said chamber, a collar spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communieating with said collar, and a 2-way valve connected to said manifold for permitting a reduction of pressure in said chamber and for restoring atmospheric pressure in said chamber.

6. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant, a container spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means for temporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communicating with said collar, a 2-way valve connected to said manifold for permitting a reduction of pressure in said chamber and for restoring atmospheric pressure in said chamber, and a pressure-relief valve connected to said manifold for rapidly venting refrigerant vapors from said chamber.

'7. Apparatus for freezing out components from a gaseous mixture, comprising a chamber adapted to contain a vaporizable refrigerant, a container open at one end disposed in said chamber, a collar spaced from and surrounding said container adjacent its open end, one end of said collar being sealed to said container adjacent its open end and the other end of said collar being open, means fortemporarily sealing said container in said chamber with the open end of the collar in communication with said chamber, a manifold communicating with said collar, a 2-way valve connected to said manifold for permitting a reduction of pressure in said chamber and for restoring atmospheric pressure in said chamber, a pressure-relief valve connected to said manifold for rapidly venting refrigerant vapors from said chamber, and a removably stoppered inlet connected to said manifold for introducing refrigerant into said chamber.

8. A method for condensing components from a gaseous mixture which comprises passing said gaseous mixture in heat exchange relationship and out of contact with liquid nitrogen at a temperature lower than the temperature at which the gas will condense, and maintaining the liquid nitrogen in heat exchange relationship and out of contact with liquid nitrogen at a reduced pressure to control the temperature thereof.

9. A method for condensing components from a gaseous mixture which comprises passing said gaseous mixture in heat exchange relationship and out of contact with liquid nitrogen at a temperature below 196 C. and maintaining the liquid nitrogen in heat exchange relationship and out of contact with liquid nitrogen at a reduced pressure to control the temperature thereof. ROBERT L. SLOBOD.

REFERENCES CITED The following references are of record'in the file of this patent:

UNITED STATES PATENTS Folsom Nov.'19, 1948 

1. APARATUS FOR FREEZING OUT COMPONENTS FROM A GASEOUS MIXTURE, COMPRISING A CHAMBER ADAPTED TO CONTAIN A VAPORIZABLE REFRIGERANT, A CONTAINER OPEN AT ONE END DISPOSED IN SAID CHAMBER A COLLAR SPACED FROM AND SURROUNDING SAID CONTAINER ADJACENT ITS OPEN END, ONE END OF SAID COLLAR BEING SEALED TO SAID CONTAINER ADJACENT ITS OPEN END AND THE OTHER END OF SAID COLLAR BEING OPEN, MEANS FOR TEMPORARILY SEALING SAID CONTAINER IN SAID CHAMBER WITH THE OPEN END OF THE COLLAR IN COMMUNICATION WITH SAID CHAMBER, AND MEANS ASSOCIATED WITH SAID COLLAR FOR PERMITTING A REDUCTION OF PRESSURE IN SAID CHAMBER. 